Process of producing alkali-metal hydroxids



nn-ira e; salaries eaaanr snares.

SAMUEL s. SAJDTLER, or SPRINGFIELD rownsmr, monre'oianar COUNTY, PENN- snvanra.

rnoonss or PRODUCING ALKALI-ME'IALIHYDROXIDS.

No Drawing.

To all whom it may concern:

Be it known that I, SAMUEL S. SADTLER, a citizen of the United States, residing at Springfield township, in the county of Montgomery and 'State of Pennsylvanla, have invented certain new and useful Improvements in Processes of Producing -Alkali-Metal Hydroxids, of which the following is a specification.

This invention relates to processes of making alkali metal hydroxids and has special reference to a process of producing such hydroxids and particularly caustic soda by a simple and inexpensive process and from mately the proportions indicated by the fol- -materials which are obtainable in abundance and-at a low cost. I

In the practice of my process, I employ a dialkali-metal phos )hate such as disodlum phosphate (Na HP and to this I add an alkaline earth-metal hyroxid, ordinarily calcium hydroxid in the, form of milk of lime, preferably mixing the materials in approx1- lowing equations (b) 2Na HPO,+3Ca(OI-I) LNaOH-i-Ca (04) 211 0.

be disadvantageous in the second stage of' theprocess. It will be understood, therefore, that to practice the process satisfactorily and economically, the proportion of calcium hyclroxid should not be materially less than that indicated byequation a-nor materially greater than that indicated by equation I).

The most advantageous proportions of disodium phosphate and calcium hydroxid Specification of Letters Patent. -Patented Aug, 31, 192(3), Application fil ed March 21, 1919. Serial No. 284,064. Y

- to be used depends upon the manner in which the second stage of the process is to be carried out. If an alkali metal sulfate such I as sodium sulfate, is to'be employed, the approximate'proportions indicated by' equation a should be used and if sulfuric acid and an alkali metal sulfate, such as'sodium sulfate, either separately or combined in an acid alkali metal sulfate, such as sodium acid sulfate, are to be employed, the proportions should be approximately those indicated by equation i As, in the practice of the second stage of my process, 'I prefer for reasons of economy to employ niter-cake, it will be understood that in the preferred commercial practice of amount of the hydroxid to the extent of any impurities that might be present therein. In the case of reaction I), to 2845 pounds of the disodium phosphate calculated as the anhydrous salt, I use approximately 222 pounds ofpure calcium hydroxid.

In the first stage of my process, as illustrated by equations a and b, the disodium phosphate and milk of lime are heated and preferably boiled until the indicated reactions occur, the reactions ordinarily being completedin a few minutes, depending in some measure upon the temperature to which the mixture is heated. The materials may be heated under superatmospheric pressure but this is not necessary. In each case, the products of the reactions are sodium hydroxid and a Water insoluble compound of calcium and phosphoric acid. In carrying out this stage of the process, according to equation a, the calcium phos hate produced is dicalcium phosphate a H (1 0 while that produced by equation I) is tricalcium phosphate Ca (PO;)

The sodium hydroxid liquor is separated from the insoluble calcium phosphate and concentrated to any desired strength by evaporation. Any unchanged disodium phosphate remaining in the dicalcium phosphate may be washed out and the Wash liquor treated with the necessary amount of milk of lime. Similarly, any unchanged disodium phosphate in the separated sodium hydroxid solution may be gotten rid of by the use of the necessary amount of milk. of lime, the calcium phosphate being precipitated.

As disodium phosphate readily reacts with calcium hydroxid it is a relatively easy matterto get rid, of practically all of the disodium phosphate Without using a material, or ordinarily, any appreciable excess of calcium hydroxid, in a two-step operation.

In the second stage of my process, the calcium phosphate which is either dicalcium or tricalcium phosphate, produced in the first stage, is treated with an alkali metal sulfate, as sodium sulfate, and 'if the tricalciumphosphate is employed, it is preferably treated with both sodium sulfate and sulfuric acid, eitherseparately or combined' In making use ofdicalcium phosphate, I' treat it at an elevated temperaturel'with a solution of sodium sulfate, of any desired 'strengthyas for example, of 20 B'., in the approximate proportions indicated by the following equation To 272 pounds by weight of pure dicalcium phosphate (Ca H (PO,) I use ap-' In this treatment, it is notnecessary to I apply heat .to themixture, but heat may be applied to hasten the reaction if desired.

(see reaction 0.)

.Instead of carrying out the last two reactionsseparately, I prefer to effect the production of the disodium phosphate 'in a single operation, making use of sodium sulfate containing sulfuric acid, known commerclally as niter-cake and in this case, re-

. actions 6 and d proceed simultaneously.

; In making use of niter-cake, which, as

stat-ed, contains both the sodium sulfate and the sulfuric acid required in reactions 0 and d, to 310 pounds of pure tricalciumsulfate (Ca (PO I use approximately 389 may be obtainedat lower temperatures.

The resulting disodium phosphate solupounds of niter-cake, containing about 28 per cent. of available sulfuric acid. The

process may be carried out with a little more acid or a little less, but my preferred forth; that is to say, a little more than the theoretical amount of sodium sulfate or sodium sulfate and sulfuric acid, as indicated in the reactions and for practical reasons I 'find'it best to use some excess.

Owing to the incompleteness of the reaction of dicalcium phosphate. and sodium sulfate, successive applications of the sodium sulfate, or niter-cake are ordinarily necessary. Such successive applications are carried out by the well known methods of series extraction or digestion. I also prefer to treat the materials in this stage of the process at above a boiling temperature, preferf ably under a pressure of about three atmospheres, although some measure of success tion' is preferably separated from the calcium sulfate at normal press'ureand at a boiling temperature but the separation may advantageously be made under superatmospheric pressure, if desired, and formechanical reasons, this might be advantageous in somecases.

. The calcium sulfate produced after being preferably washed and" dried, is useful in the arts.

From the foregoing description, it will be understood that the principal product sought to be obtained by 'myprocess isan alkali metal hydroxid, ordinarily caustic soda, the

calcium sulfate or gloss white being a byproduct, and that the phosphoric acid salt produced is obtained as an intermediate productand is converted into a dialkali metal phosphate, ordinarily disodium phosphate, which is employed-in the-first stage of my process and takes its part in the 1cycleof operations, theoretically without oss. Y

I I have found that some measure of suc- The dicalcium phosphate is then treated with sodium sulfate, as already described.

cessmay be obtained by the-use of any other alkali metal salts cap'ableofuniting with the dicalcium or other 'dialkaline earth metalphosphate employed inthe second stage of my process to form a substantially insoluble salt with the-calcium or other alkaline earth metal present therein. For example, some measure of success is obtainable by using an alkali metal sulfite, citrate or tartrate, as, for example, sodium sulfite, sodium citrate orsodiurn tartrate,.in place of sodium sulfate and Where calcium hydroxid is employed in the first stage of 'my process, the

results are such as to indicate that this procedure is of substantial practical value =acid capable of transforming tricalcium" I have also found that some measure of success may be obtained by the use of any 1 phosphate into dicalcium phosphate instead of. sulfuric acid and that such acid may be employed either free or combined in an acid salt." Among the acids which may be used templated as within the purview of my in-' vention and that the proportions of reagents and details of procedure as herelnbefore specifically set forth may be varied without departing from the spirit of my invention .nietal hydroxid which consists in reacting consists in reacting upon disodium. .phosor the scope'of the subjoined claims.

Having described my invention, I claim: l. The process of producing an alkali upon disodium phosphate with calcium hydroxidin the approximate proportions of from 1&8 to 222 parts byweightof the hydroxid to 284 parts-by weight Of'theiphos phate.

2. The herein described process which consists in reacting upon a dialkali metal phosphate with an alkaline earth metal hy droxid, subjecting the solid portion of the product to the action of an alkali metal salt,

of an acid adapted to form substantially water insoluble salt with .c'alciu'mat an elevated temperature, and separating the solid from the liquid portion of the product. 3. The herein described process which consists in reacting upon a dialkali metal phosphate with an alkaline earthmetal hydroxid, subjecting the solid portion of the product to the action of an alkali metal salt of an acid adapted to form a substantially water insoluble salt with calcium at above 100 C. and under superatmospheric pressure, and separating the solid from the liquid portion of the product. $4. The herein described process which consists in reacting upon a dialkalimetal phosphate with an alkaline earth metal'hydroX'id, subjecting. the solid portion'of'the product to the-action ofan alkali metal salt of an. acid adapted to form a substantially- Jwater insoluble salt with calcium at an elevated temperature, and an acid, and separatproduct.

.ing' the solid portion of the product tothe 'tionof theproduct.

5. The herein described process which consists -in reacting upon a di-alkali metal phosphate-with an alkaline earth metal hy- 'dro' id, subjecting the solid, portion 'of the product to the actionof sodium sulfate, and separating the solid from the liquid portion of the product;

. approximate proportions of 310 parts by weight of the former to 389 parts by weight of the latter, and separating the solid from the liquid portion of the product.

7. The herein v described process which consistsin reactin upon a dialkali metal phosphate with ca cium hydroxid, "subjectaction of an alkali metal; salt of an acid adapted to form asubstantially water insoluble salt with calcium at an elevated temperature,- and separating'the solid from the liquid portion of the product. I

8;. The herein described process whichphate with an .alkaline earthmetal hydroxid, subjecting the solid portion of the product I to the action of an alkalimetal'salt of an acid adapted to form a substantiallywater insoluble salt with calcium at above lQQ? (1., and separating the solid from the liqui'd'por 9. The herein described process which consists in reacting upondisodium' phosphate with calcium hydroxid, subjecting the solid portionof the product to the action of an alkali metalsaltof an acid adapted to forma substantially water insoluble salt with calciumat above 100 C. and separatingthe solid from the liquid-portionofthe product. a 10. The herein described process which consists in reacting upon disodium phos 1'05 phate with calcium hydroxid in the approximate proportions of 222 parts by weight of the-hydroxid o 284 parts by Weight ofthe phosphate, sujecting the solid portion of the product to the action of niter-cake; in the 1-10 In testimony whereof afiix my signature 11 5. .in presence of tWOWitIlGSSQS. 7

SAMUEL S. SADTLER. Witnesses v OnAs :Wm'rrms, Gfrno. A. Rnrrz. 

